Small increment ribbon feed



A. H. CAUDILL ETAL 3,432,020

SMALL INCREMENT RIBBON FEED Filed Jan.

J I mu I 91 55:.

L L D U A SC R mH N E 0 N L L A WILLIE GOFF, JR. (TM

ATTORNEY March 11, 1969 FIG. 2

United States Patent 3,432,020 SMALL IN CREMENT RIBBON FEED Allison H. Caudill and Willie Golf, .lr., Lexington, Ky.,

assiguors to international Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Jan. 6, 1966, Ser. No. 519,098

US. Cl. 197151 3 Claims Int. Cl. B41 3 33/28; B65h 23/14 ABSTRACT OF THE DISCLOSURE Relatively uniform, small increment metering of typewriter ink ribbon onto a spool is accomplished without the usual pinch roll and capstan by reliance on the dynamics of a system including a source of incremental motion, a resilient coupling, and a slipping transmission all connected in series power transmitting relationship to the spool and further including a brake device acting against the ribbon delivered to the spool to maintain a substantial tension in the ribbon. The increase in eifective spool diameter as ribbon is wound modifies the dynamic response of the system to the incremental input motion to compensate for the inherent geometrical non-uniformity ordinarily experienced in winding web directly onto spools.

Our ribbon mechanism provides small feed steps (in the order of 0.010 inch) with adequate precision without the use of complex measuring apparatus. Our mechanism is unique in its simplicity, permitting it to be readily added to existing ribbon feed devices to provide multiple ribbon capabilities.

US. patent application Ser. No. 171,188 entitled Transfer Medium and Method for Making Same, filed by H. T. Finley and K. H. Froman, Feb. 5, 1962, now abandoned; and application Ser. No. 428,892 entitled Spongeous Typewriter Ribbon filed by Hugh T. Finley and William H. Horne, i an. 25, 1965, each disclose typewriter ribbons having the characteristic of producing print approaching the quality of the well-known total release or carbon ribbons, but having the ability to print with several overstrikes on the same area. Ribbon of this type, however, cannot effectively be directed substituted in a machine adapted to pass a total release ribbon in full character increments one time through, as the overstrike capacity is completely wasted. It is thus desirable to modify the total release ribbon feed to permit overstriking the ribbon during its Single pass to take advantage of its best characteristic. The operator is thus provided with the selection, on one machine, of highest quality print, or, more economical, good print. To achieve the more economical result, however, it is necessary to advance the ribbon by very small increments so that successive strikes will overlap preceding strikes to some extent, thus providing a multiple strike on the same ribbon area.

Existing single pass ribbon feed mechanisms employ some form of precision feed increment measuring such as a pawl and ratchet that take a precise step each advance cycle to move the ribbon some proportional amount. For example, the pawl and ratchet may control a capstan to eliminate feed variations due to diameter change of the take-up spool, as disclosed in the IBM Technical Disclosure Bulletin, vol. VI, No. 4, September 1963, page 17. Mechanically metering extremely small incremental steps, as required for a single pass overstrike type of ribbon feed, requires a wholly new feed drive that is not readily adaptable to machines already in service. The cost of a more complex feed system also must be weighed against the advantages of multiple ribbon selection.

Accordingly, it has been an object of our invention to ice provide an inexpensive but adequately precise and reliable, small increment ribbon feed.

Another object of this invention has been to provide a ribbon feed having precision that is independent of variations in temperature and humidity.

Another important object of this invention has been to provide a ribbon feed for an overstrike type of ribbon that is capable of feed increment adjustment to permit operator control of print quality.

A further object of this invention has been to provide a ribbon feed control attachment for adapting existing single pass ribbon feed mechanisms for operation with an overstrike type ribbon.

Our invention combines a slipping torque transmission in series with an incrementally pulsed resilient input drive and a ribbon dr-ag brake which maintains a substantial tension on ribbon supplied to a takeup spool. The power source and slipping clutch are provided by an existing incrementing power source for a capstan ribbon feed, like that disclosed in the aforementioned IBM Technical Disclosure Bulletin. A take-up spool drive as'disclosed therein includes a slip-force-limited spring belt transmission connected with the incremental power source. We employ this existing mechanism to provide a source of time and magnitude limited torque that is supplied to the take-up spool each occasion a ribbon advance is required.

A tension trapping brake, preferably in the form of a pair of guide or tracking posts, provides a controlled resistance to ribbon winding. The ribbon passes about the tracking posts and doubles back upon itself such that the brake retains ribbon tension at the take-up spool.

between feed cycles; hence the term, tension trapping.

The incremental power source, the spring belt transmission, the take-up spool, and the tension trapping brake define a spring-mass system that is driven each feed cycle. The response of the system to the fixed incremental drive, varies with the eifective ribbon take-up diameter to compensate for the otherwise expected feed increase with diameter increase and thereby maintain a relatively constant linear feed increment.

Another phase or concept of our invention involves the provision of an automatic friction control device to compensate for frictional changes in the ribbon characteristics due to temperature and humidity. Such changes are accommodated by mounting the brake forming guide posts on a pivotally yieldable bracket arranged to permit the posts to move upon increased friction in a direction so as to slack off some of the contacting angle. The resultant frictional force is thereby decreased as required to produce a stable feed. The automatic compensation mechanism further employs a manually adjustable datum set that sets the desired incrementing step by reducing or increasing the angular orientation of the braking guide posts. Accordingly, the operator can select a greater incremental step when it is desired to produce higher quality print with resulting reduced total character yield, or can select a lower quality print by reducing the ribbon feed increment for operations such as rough drafts, etc.

The foregoing objects, features and advantages of our invention will be more apparent to those skilled in the art upon reading and understanding the: following more specific description of a preferred embodiment of our in vention wherein reference is made to the accompanying drawing of which:

FIGURE 1 is a partial y broken away perspective view of a ribbon feed mechanism for a typewriter constructed in accordance with our invention; and

FIGURE 2 is an enlarged plan view of the tension trapping brake shown as part of FIGURE 1.

More specifically, there is shown a typewriter or other impact printer 10 having a platen 11 which cooperates with a print head 12 to define a printing station 13. An appropriate printer is disclosed in US. Patent 2,919,002 entitled Selection Mechanism for a Single Printing Element Typewriter issued to L. E. Palmer on December 29, 1959. Printing is accomplished through the use of an inking or transfer ribbon 21 that preferably is made in accordance with either of the aforesaid US. patent applications, but the feed mechanism can advantageously be employed with any ribbon, tape, or other continuous web.

The ribbon 21 is fed by the novel mechanism of our invention which is mounted on a bracket or support plate 29.

The ribbon 21 is supplied from a spool or reel 22 rotatably mounted on pin shaft 23 and is guided through ribbon lift fingers 24 past the printing station 13. A drag brake 25 that is pivoted about stud 25a and biased clockwise by a spring 25]), engages the outer periphery of the ribbon 21 on spool 22 to prevent overrun thereof which would otherwise cause loosening of the supply ribbon 21. The ribbon 21 downstream of the printing station 13 is tracked around guide posts 33' and 32 of a tension trap friction drag brake and a guide member 26 to a takeup spool or reel 27 that is rotatably mounted on a pin shaft 28. A typical dimensional relationship between the brake guide posts 31 and 32 and member 26 is shown in FIGURE 2 with reference to the following tabulation of significant dimensions.

a inches 2.50 b do .165 c do .125 u. degrees 68 B do 98 'y do 38 These dimensions are illustrative only and apply strictly to specific materials, force levels, feed increments and other ancillary conditions. It is principally important to note that the ribbon 21 is doubled back to contact itself at point 33, but that the various angles still permit ribbon feeding under some force conditions.

A source 40 of incremental driving power or torque is provided of substantially the same construction as described in the aforesaid IBM Technical Disclosure Bulletin and includes a stepping pawl 41 and a ratchet wheel 42 having holes 43 therein defining rachet teeth therebetween. Pawl 41 is pivotally connected to cam follower 41a by stud 41b and is urged into ratchet engagement by a spring 410. A pin 41d is urged by a spring 41c into engagement with a cam 41 that is driven through a complete revolution during each print operation of the printer fit). A slip limited torque or force transmission, including pulleys 44 and 45, and an elastic resilient energy storing means or garter spring 46, connect the ratchet wheel 42 to the pin shaft 28 to provide a time and magnitude limited torque input to the take-up spool 27. It will thus be seen that every operation of the pawl and ratchet 41, 42 will cause the application of a winding torque to take-up spool 27 which will result in a feed incrementing of the ribbon 21 resisted principally by the brake 30. Our novel feed mechanism does not interfere with an existing feed for total release ribbons including ratchet driven capstan 47 and pinch roll 48 held against the capstan by a spring 49. In fact, the two mechanisms are alternately usable at the operators selection.

While the input to pulley 44 is a constant angular impulse each feed cycle, it is desired to cause a variable angular motion of the take-up spool 27 to compensate for its variation in diameter, and thereby generate a constant linear ribbon feed. Accordingly, when the spool 27 is empty it is necessary that it turn through a greater angle than when it is full.

The acceleration characteristic of the system defined by transmission spring 46, and the moment of inertia of the spool 27 and ribbon Z1. thereon, also varies with diameter, and by this variation provides the basis for the feed increment control.

To fully realize the control, it is necessary to maintain the ribbon tension near the threshold of transmission slippage, so that the ribbon tension will be available to terminate the feed early in the cycle. Brake 30 performs this function by trapping the ribbon 21 upon itself.

Although we do not fully understand the theory by which our mechanism operates, we have observed that the operation results from the intercooperation of a slipping transmission, a spring driven mass having a variable diameter, and a tension trapping drag brake acting on the ribbon. Our results have shown a remarkable uniformity in ribbon feed considering the simplicity of the mechanism involved.

The mechanism thus far described is somewhat sensitive to temperature and humidity changes, as these factors afiect coefi icients of friction between the various frictionally engaged parts. Our two post, tension trap brake 30 has the highly versatile characteristic of providing a readily variable drag simply by changing the angular relationships between the ribbon Z1 and the two posts 31 and 32. We have mounted the drag brake 30 on a bracket 34 that is pivoted about stud 34a defining an axis 34a parallel to the posts 31 and 32. The bracket 34 is biased by a spring 35 to cause the posts 31 and 32 to present a large angle 'y as shown in FIGURE 2. Increase in angle 7 corresponds to an increase in drag. tlf the various coeflicients of friction increase to where the ribbon feed mechanism 10 would lock up rather than permit slippage of the ribbon 21, the braking posts 31 and 32 directly sense the ribbon tension and the bracket 34 yields, moving against the bias of spring 35 to reduce angle 7 and hence provide a lesser drag on the ribbon 21. The system is automatically compensating and requires no attention from the operator. Ideally, the tension variation throughout the feeding of an entire ribbon should not cause significant change in angle 7. In practice, the variation tends to allow excess feed during the early or empty spool portions of feeding a ribbon.

The ink ribbons disclosed in the aforesaid US. patent applications have the highly desirable characteristics of providing good print quality with several overstrikes, and even better or excellent print quality with fewer overstrikes. We have provided an adjustable but relatively fixed datum for the bracket 34 in the form of limit stop 36. Limit stop 36 is threadedly supported by an upturned ear 20a of plate 20 to permit axial adjustment by manual rotation. Stop 36 abuttingly engages an upturned tab 34b of pivoted bracket 34- that is offset forwardly of the pivot stud 34a to permit manual positioning of the bracket 34 against the bias of spring 35. Angle 'y is thereby made variable by the operator to vary the drag posed by the brake 30 and thus increases or decreases the feed stroke to select the desired number of print over-strikes and print quality. Acordingly, the operator can set the feed mechanism for either the highest quality print available from the ribbon, the highest character density, or something inbetween, depending upon the requirements of the particular job being prepared.

Those skilled in the art will recognize that we have provided a remarkably simple mechanism for producing an inexpensively obtained incremental motion, and that our mechanism is not only simple in manufacture and use, but is highly versatile as to the control characteristics obtainable.

We claim:

1. An impact printer ribbon feed mechanism comprising:

a supply of inking ribbon,

a take-up spool rotatably supported for windingly re ceiving said ribbon,

guide means tracking said ribbon past a printing station,

a source of incremental driving power,

a transmission including resilient energy storing means 2. An impact printer as defined in claim 1 wherein in series power transmitting relationship with said said relatively fixed datum comprises: incremental power source, said transmission resilient means for adjusting the datum of said mounting energy storing means and said take-up spool being bracket to provide adjustable incremental stepping. interconnected for the transfer of limited force there- 5 3. An impact printer as defined in claim 1 wherein between, said transmission and force limited connection comprises mutually exclusive, selectively operable first and seca garter spring-pulley assembly.

0nd means for controllably engaging said ribbon, said first means comprising a pinch roll and capstan References Cited directly coupled to said incremental power source UNITED STATES PATENTS for predetermined incremental movement thereby, v and said second means comprising brake means for 3 g gg zg zg g zgf tensm the supphed 803,400 10/1905 Conley 242 75.2 X said brake means comprising a friction brake having 1069985 8/1913 Steele 197 151 a 1,133,309 3/1915 Nall 242-752 pair of guide posts about which the ribbon is 1251081 12/1 17 M tracked said posts being supported on a mounting 9 eyer 226*195 X 2 554 028 5/1951 Helmond 197-151 bracket and oriented relatlve to the ribbon and to 3022724 2/1962 W rth 197 151 each other whereby the ribbon is caused to double o X back and engage itself at least at one point on one 20 OTHER REFERENCES of Posts; IBM Technical Disclosure Bulletin, 'vol. 7, No. 7, Demeans prvotally supporting said mounting bracket for camber 196 PP 3 and movement, about an ,axls Parallel to Sald Posts; IBM Technical Disclosure Bulletin, vol. 6, No. 4, Sepmeans defining a relatively fixed datum for abutting tember1963, pp 17and18 said bracket, and means resiliently urging said bracket towards said ROBERT U Primary Examinen datum and in opposition to ribbon tension induced forces whereby said forces, when excessive, can pivot ERNEST WRIGHT Assistant Exammer' said bracket against said resilient urging means to Us Cl XR automatically modify the angular orientation between said posts and the ribbon. 

